Package org.eclipse.persistence.sdo

Class SDOResolvable

java.lang.Object
org.eclipse.persistence.sdo.SDOResolvable
All Implemented Interfaces:
ExternalizableDelegator.Resolvable, Externalizable, Serializable
public class SDOResolvable extends Object implements ExternalizableDelegator.Resolvable
INTERNAL:

Purpose:

This class performs serialization/deserialization of an SDODataObject.

Responsibilities:

  • Provide/override default Java serializable access to a DataObject
Serialization Process

Serialization and de-serialization of objects occurs during DAS transactions, Web Service transactions in the SOAP envelope, EJB container passivation, web container session saving or directly in an application using the function ObjectOutputStream.writeObject(Object). The Serializable and Externalizable framework handles automatic or user defined reading/writing of streams depending on which interface functions are realized in the implementing classes.

The Serializable interface has no operations - therefore a class that implements it needs to add no additional functionality. Why do this? - For security. The security manager in the JVM will only serialize objects at runtime if they are flagged as Serializable (or Externalizable) so that by default java classes do not expose themselves to serialization. (See p49 of Java Security 2nd edition).

There are 3 levels of serialization control.

  • 1) Default Serialization
    Here we make the class implement Serializable, mark non-serializable fields as transient and implement no new functions.
  • 2) Partial custom Serialization
    Here we make the class implement Serializable and implement the optional functions writeObject and readObject to handle custom serialization of the current class while using the default serialization for super and subtypes.
  • 3) Fully customized Serialization - current implementation.
    Here we make the class implement Externalizable and implement the functions readResolve, writeReplace, readExternal, writeExternal. Supertypes and subtypes must also implement these functions.

The SDO 2.01 specification details the high level structure of the serialization format on page 64, section 6 - Java Serialization of DataObjects. The process will involve gzip serialization of the xml data with UTF representation of the Xpath address of the current DataObject inside the entire tree along with its identification as root/no-root in binary 1/0 format as follows.

  • Security:
    The following public functions expose a data replacement vulnerability where an outside client can gain access and modify their constants. We may need to wrap the GZIP streams in some sort of encryption when we are not using HTTPS or SSL/TLS on the wire. public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException public void writeExternal(ObjectOutput out) throws IOException
  • Concurrency:
    Avoid synchronized classes that will queue threaded clients such as Enumeration, Vector etc. We need to discuss how this API will be used by containers like an EJB container that can invoke multithreaded clients.
  • Scalability:
  • XML Serialization Size is 4GB:
    There is a limitation set by the SDO Specification on the size of the DataObject serialization. According to the spec we must use an integer to define the size of the GZIP buffer that is serialized. This size is limited to +/- 2GB. This limitation is actually set by the JVM itself because a call to buffer.length returns a signed 32 bit integer.

  • Performance:
    Using custom serialization via the Externalizable interface is 30% faster than the default java serialization because the JVM does not need to discover the class definition.
See Also:

  • Field Details

    • DEFAULT_ROOT_ELEMENT_NAME

      public static final String DEFAULT_ROOT_ELEMENT_NAME
      Root element name for all DataObjects undergoing serialization = sdo:dataObject
      See Also:

    • SDO_HELPER_CONTEXT_ID_IDENTIFIER

      public static final int SDO_HELPER_CONTEXT_ID_IDENTIFIER
      root object with helper context id identifier
      See Also:

    • SDO_ROOT_OBJECT_IDENTIFIER

      public static final int SDO_ROOT_OBJECT_IDENTIFIER
      root object serialization type identifier = 1
      See Also:

    • SDO_INTERNAL_OBJECT_IDENTIFIER

      public static final int SDO_INTERNAL_OBJECT_IDENTIFIER
      internal object serialization type identifier = 0
      See Also:

  • Constructor Details

    • SDOResolvable

      public SDOResolvable()

    • SDOResolvable

      public SDOResolvable(HelperContext aContext)
      Default constructor for deserialization

    • SDOResolvable

      public SDOResolvable(Object target, HelperContext aContext)
      Constructor for serialization

  • Method Details

    • readResolve

      public Object readResolve() throws ObjectStreamException
      Purpose: This function is called after readExternal to return the recently deserialized object retrieved from the ObjectInputStream. Here there is an opportunity to replace the object with a Singleton version
      Specified by:
      readResolve in interface ExternalizableDelegator.Resolvable
      Throws:
      ObjectStreamException

    • writeExternal

      public void writeExternal(ObjectOutput objectOutput) throws IOException
      Purpose: Serialize an SDODataObject to an ObjectOutputStream This function is mandated by the Externalizable interface. It writes binary data in the same order as was will be read back in readExternal(). Prerequisites: An object has already been constructed and associated with the theSDODataObject member
      Specified by:
      writeExternal in interface Externalizable
      Throws:
      IOException

    • readExternal

      public void readExternal(ObjectInput objectInput) throws IOException, ClassNotFoundException
      Purpose: Deserialize from an ObjectInputStream into an SDODataObject This function is mandated by the Externalizable interface. It reads back binary data in the same order as was written in writeExternal(). An object has already been constructed with the no-arg constructor before this function fills in the member fields. The deserialized object will be returned later in a call from the ObjectInputStream to readResolve()
      Specified by:
      readExternal in interface Externalizable
      Throws:
      IOException
      ClassNotFoundException

    • getHelperContext

      public HelperContext getHelperContext()
      Returns:

    • setHelperContext

      public void setHelperContext(HelperContext helperContext)
      Parameters:
      helperContext -